1. Field of the Invention
The present invention relates to a reticle constructed to measure a rotation error of the reticle on a wafer caused by an alignment error of the exposure equipment, and a method for measuring the rotation error of the reticle by use of the reticle itself.
2. Description of the Prior Art
In a contact printing carried out in a manner where a mask is in contact with a photoresist film during a light exposure step, there is a problem that the mask is quickly degraded after several uses thereof. In order to avoid such a problem, a projection printing has frequently been used. A mask (hereinafter referred to as a reticle) used in this projection printing method, does not come into contact with a sample. Accordingly, the reticle can be used repeatedly without any degradation thereof. Such a reticle used for a projection system may include an array of individual circuits or may be only a part of the array. In the latter case, the pattern of the reticle is reduced and focused onto a wafer. Using a precise step-and-repeat process, an array is formed on the wafer.
In a highly integrated device, therefore, a rotation error of the reticle may be a very important factor. To this end, the reticle is generally provided with a vernier for measuring the rotation error of the reticle.
FIG. 1 is a plan view illustrating a conventional reticle capable of measuring a rotation error thereof. This conventional reticle will now be described in conjunction with FIG. 1.
As shown in FIG. 1, the reticle has a square positive area 3. Along three edges of the positive area 3, scribe lines 2 are formed. A mother vernier 4 and a son vernier 5 are provided at the scribe lines 2 formed along the left and right edges of positive area 3, respectively. The verniers 4 and 5 have a square shape. The verniers 4 and 5 are disposed on a horizontal line.
In this reticle, however, the mother and son verniers 4 and 5 are formed at positions removed from the center of the reticle (namely, positions removed from the center of a lens equipped in the exposure equipment), respectively. As a result, the mother and son verniers 4 and 5 are disposed such that they do not overlap in the center of the lens where a small lens distortion error is involved, but overlap at a peripheral portion of the lens where a large lens distortion error is involved. Consequently, it is difficult to accurately measure the rotation error of the reticle.